The present invention relates to a track roller and more particularly, to a self-aligning track roller for accommodation to variable track surfaces comprising a co-engaging inner race and outer race movable relative to one another wherein an elastomeric element such as a ring is disposed between respective ends of the inner and outer races so as to bias the inner race into alignment with the outer race. Further, the inner race has a bearing surface provided with a self-lubricating material which is engageable with and movable relative to the bearing surface of the outer race.
At present, track rollers being used incorporate a crown radii on the outer diameter of the outer race to compensate for track deflections and irregularities. This reduces the contact area between the roller and the mating surface of the track. An increase in contact bearing pressure results due to the reduced contact area which has caused excessive wear and distress to the track surface.
Further, the conventional track roller bearings are constructed with rolling elements positioned between the inner and outer races and require a lubricant such as grease. Addition of lubricant to the rolling elements is periodically required to maintain the operational performance and to add corrosion resistance. Such bearings are subject to failure where fracturing of the rolling elements and spalling of the inner race occur. In addition, the performance of these track roller bearings depends on the effectiveness of seals incorporated therein which ensure that the grease lubrication is maintained within the varying surface area, proper, and that the grease lubrication is not contaminated from external sources.
It is known to incorporate a self-lubricating liner system as an alternative to the rolling element track roller surface of the outer race so as to operate against the bearing surface of a hardened inner race. These bearing assemblies have the advantage that they do not require periodic lubrication and they have a generally higher rolling load capacity. In addition, static radial load capacity of these bearing assemblies is substantially higher than the rolling element bearing assemblies with high thrust capacity being ensured by the use of the separate self-lubricating liner system. These self-lubricating type bearing assemblies are discussed for example in U.S. Pat. Nos. 4,048,370 and 4,134,842.
The self-lubricating liner systems with the liner attached to the inner diameter of the outer race were designed in accordance with the belief that the wear experienced during the life of the bearing system could be distributed over the full circumference of the liner and thus result in extended surface life. Nevertheless, it has been found that because of the rotation of the outer race liner in relation to the stationary inner race and the unidirectional load application, liner systems with a compression modulus of up to about 1 million psi are subjected to material deflection. More particularly, the mismatch of the inner race circumferential surface to the outer race by differential tolerances and the thickness of the liner system provide the mechanism which permits local deflection of the liner as the outer race moves relative to the inner race when loaded. Therefore, under a steady applied load, while moving in relation to the inner race, high shearing action and tensile forces are imposed on the liner immediately in front of the progressing load action of the inner race. This is known as ploughing. When combined with fluid contamination, the liner is further distressed due to the wedging action of fluid in front of the advancing inner race slider.
Lubricating material affixed to the outer race in a track-roller bearing assembly is subjected to distortion and consequent reduced service life relative to the arrangement of the present invention. The induced liner deflection when loaded by the inner race during rotation of the outer race adversely affects the bond between the lubricating material and the outer race, and as the bond fails, the lubricating material is pinched between the inner and outer races without any support and tends to be squeezed out.